To immobilize part of the vertebral column, in particular to treat the degeneration of an intervertebral disc, it is well known to use vertebral osteosynthesis equipment comprising anchor members for anchoring to the vertebrae (pedicular screws and/or laminar hooks), connecting rods making it possible to connect said anchor members to one another, and connectors making it possible to connect said connecting rods to said anchor members.
An anchor member is frequently “polyaxial,” i.e. comprises a threaded proximal stud articulated relative to an anchoring base, the stud comprising a distal articulation portion and the anchoring base forming a proximal cavity in which said distal articulation portion is received. Patent publication No. EP 0 986 339, in the applicant's name, illustrates an anchor member of this type.
In the known equipment, the proximal studs of the anchor members are, in general, freely movable in the proximal cavities of the anchoring bases, which leads them to adopt by gravity inclined positions relative to the anchoring bases when the anchor members are implanted. These inclined positions are most often bothersome in the implantation site, which is deep and has small dimensions.
The documents US 2003/163133, US 2006/229606, US 2010/100137, EP 0 861 636 and U.S. Pat. No. 5,800,435 show various existing devices that do not resolve this essential drawback.